Recently, due to demand of biodiesel, a large quantity of glycerol is being produced, and studies on the application thereof are progressed.
Among them, preparation of lactic acid using glycerol has been suggested. For example, a method of preparing lactic acid from glycerol under sever conditions of 300° C., 80 atm through a hydrothermal reaction using alkali base such as NaOH, KOH is known (U.S. Patent Application Publication No. 2009/0088589; U.S. Patent Application Publication No. 2010/0047140; Ind. Eng. Chem. Res. 2009, 28, 8920; Chemistry letters 2005, 34, 1560).
However, this method has disadvantages in that an additional process for separating a catalyst is required because the catalyst is dissolved in the product due to the use of a homogeneous catalyst such as NaOH, KOH, and a large quantity of impurities are produced. Furthermore, since the catalyst separation process is very complicated and difficult, operatability is lowered and the process is uneconomical in terms of the cost.
To solve the problems according to the use of a homogeneous catalyst, a method of preparing lactic acid through hydrogenation of glycerol using an active carbon-supported heterogeneous catalyst such as Pt, Ru, Au is known. However, this method also has disadvantages of low conversion rate and selectivity (Journal of catalyst 2007, 249, 328; Journal of catalyst 2007, 251, 281).
Meanwhile, in a stripper (stripping solution) for removing a photoresist layer in the manufacture process of fine circuit of semiconductor integrated circuit and liquid display device, NMP(N-methylpyrrolidone), DMAc(dimethyl acetamide), and the like are generally used as a solvent. However, since the solvent is highly toxic, lactamide compounds have been used as a solvent replacing the NMP, DMAc for operability and environmental-friendliness (Korean Laid-open Patent Publication No. 2009-0106992).
The lactamide compound is an environmentally-friendly low-toxic biosolvent based on biomass obtainable using glycerol that is by-product of the biodiesel. Thus, a method of increasing productivity of the lactamide compounds is being studied.
As the existing method of preparing lactamide, a method of preparing lactamide by reacting lactic acid, alkyl lactate with amines is known (WO 2009/121488, WO 2009/121489). However, when lactamide is prepared from lactic acid, lactic acid and alkyl lactate are obtained with low yield due to the above problems, and thus, yield and purity of lactamide may not be improved. Moreover, a method of preparing alkyl lactate with high yield and high purity has not been known.